Even if the camera is throwing out 2 syncs, how come the flash hooked directly to the camera doesn't trigger twice?
I'll scope my camera this weekend. Should be easy to see what's coming out of it.
Anyone live around Philly with a 1V who wants to let me try it out with my equipment?
I scoped my camera. It appears that the center pin to the edge of the hot shoe (ground in this case?) has 0 V in standby mode. When the shutter is half pressed for metering, the center pin jumps to approximately 3.3V and stays there until the in camera metering shuts off. When shutter is press down all the way, the center pin drops down to 0V and rises back up to 3.3V approx 200ms later. I say approximately because as the shutter speed gets faster, this gate narrows a bit (10 ms or so) and as it gets longer, say 1/15s, the gate stretches out to about 300 ms, 1/5s was around 380 ms, and at 1s, it was 1.16 s. The PC port showed the same behavior.
I guess the PW is interpreting the leading and trailing edge of the gate as a trigger. If this is the case, I don't know why it's not interpreting the voltage rise at the beginning of metering (and at the end of metering for that matter) as a shutter trigger. So I must be missing something. The 285HV knows how to interpret the signal in the hot shoe. And the PW knows how to interpret the M6 signal (which I need to scope). I didn't scope my M6 since it has film in it right now. I'll do it the next time its empty. Actually, I didn't think of it, but will now.
For that matter, I'll scope the pulse that the PW generates too.
I've had a similar problem with a Nikon D2xS. Ok, this model is d******, but the problem's the same. Only intermittently, but I've come to the conclusion it is the actual synch cord as I can wiggle it around a bit and it disappears.
I use the PW II with the settings set for "BOTH" on each. Is that how yours are set?
I'm curious what you were measuring on your camera; centre pin to ground should be the anode-to-cathode of a thyristor in a camera like that I believe. You must be measuring the gate voltage.
You should be measuring resistance/continuity, not voltage - when the gate voltage is applied to the thyristor it closes the pin-to-shoe circuit which is what triggers the flash.
If you are measuring thyristor gate voltage, it should match - but you may confuse yourself if you check another camera which uses a mechanical flash trigger switch and you can't find the volts :-).
All my own speculation, by the way, corrections gratefully accepted :-)
Further pondering... A thyristor latches of course; one it's been triggered to conduction by the gate voltage, it will continue conducting until (a) the gate voltage is removed and (b) the anode current drops below a threshold. In practice that means the 'falling edge' of the gate pulse is irrelevant when you have a real flash connected; once the thyristor is triggered it will conduct anode->cathode until the stored energy in the flashgun is fully discharged through the flashtube (at which point the anode current drops below the point at which the thyristor stops conducting until it's triggered again.) (A good old fashioned flash just connects the output of its storage capacitor directly to the centre pin, and the input to the flashtube to the edge pin - the thyristor/switch just connects the two together so the capacitor discharges through the tube. That's why old fashioned flashes present a few hundred volts on their centre pin.)
Last edited by tim_walls; 03-30-2008 at 06:53 AM. Click to view previous post history.
This may be another bit of useless information but......Is there a safety switch in the hotshoe? Most cameras do have them. Usually between the tension spring and the edge of the shoe. You can usually see the plastic post by peering into the edge of the shoe. The safety switch should be closed when you're testing.
Your knowledge of electronics is way beyond mine and especially with one of the newer(?) old cameras like this. With a mechanical switch it's just an NO switch. I do like the idea of the double pulse causing your quandry.
In the past I've seen a number of odd occurrences with the Canon SLR's including flash units that would work on other cameras. We assumed it was polarity differences & let it go.
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Ahh, see I come from a science background and was thinking of triggering, which is usually 5 V TTL pulses or gate pulses. I'll remeasure the impedance. I figured since Canon cameras have fancy communication with their flashes, there must be some stuff going on voltage wise. The thyristor makes sense.
It's odd that other people don't seem to have this problem, since there must have been at one time a lot of 1V's in use, and they must have been used with PW's. I'd also be surprised if the way the hotshoe works in a 1V (a modern camera) is that different from the new digital models.
And yeah, I was measuring from center pin to the edge.
There is plenty of other clever stuff going on voltage wise, but it should be via the other pins on the hotshoe. The basic hotshoe cirsuit is centre-pin to shoe, normally open closed when the shutter fires. (Of course, I wouldn't be surprised if certain signals on the other pins changed the behaviour of the center pin on an intelligent camera like the 1V.)
Assuming what you were measuring was the gate->cathode voltage though, everything you measured 'looked right'. You would expect a pulse when the 1V meters (my 1V fires the flash whenever I take a sample, at least in multi-point spot, which is what I normally use,) and then another one when the shutter fires (of varying duration, although in principle anything attached should pay attention to the rising edge only - there are no guarantees of what the falling edge will do AFAIK.)
Hmm. That's a point. Does metering mode make a difference? When I'm spot metering, the flash fires whenever I take a reading, but I don't remember getting a double flash when shooting in one of the other meter modes...
Another day goes under; a little bourbon will take the strain...
No, metering mode makes no difference. Again, to reiterate, everything works fine with the flash mounted directly to the camera. Its when the PW's are in line, they interpret the 1V's signal as 2 flashes, one at the appropriate time, and one after the shutter closes. I did some tests with long shutters speeds, and the second flash is most definitely after the mirror goes back because you can see the 2nd flash through the viewfinder.
humph, I'm confused then - the signal you measured sounds correct, so I assume either the PW is faulty or it's trying to be too clever by half (I've never used a PW - is there anything configurable about them?)
I've tried to recreate the problem with my 1V, a Vivitar 283, and with/without cheap wireless triggers, and I can't.
I have a scope and a logic analyser here - if you want me to make any measurements of my 1V to compare let me know.
Cool. Yeah, I have no problems with my 1V and 283. Its just with the PW inline. I might get back to you about measurements in a bit. I'm going to do a bit more investigation first.